An image forming apparatus such as printer, copier, facsimile, and MFP (multi-functional peripherals) may be attached with a finishing unit, to which a sheet having an image thereon is ejected from the image forming apparatus.
The finishing unit may include a perforator to perforate a hole on the sheet ejected from the image forming apparatus.
The perforator includes a reciprocal type unit having a die frame, a guide frame, and a blade, for example.
The die frame includes a die hole, and is placed under a transport path of a sheet. The guide frame includes a guide hole, and is placed over the transport path of sheet.
The die hole and guide hole are aligned in a same axial direction so that the blade can be moved in a reciprocal direction through the guide hole and the die hole.
The blade is moved in the reciprocal direction through the guide hole and the die hole to perforate a hole on the sheet, transported between the die frame and guide frame.
In order to conduct such a perforation process on the sheet, the blade may be supported by the guide frame with a given allowance, such as 10 micrometers, for example.
Furthermore, the blade and die frame are designed in a manner so that the blade and die hole have a given amount of clearance between the blade and die hole, such as 10 to 20 micrometers, for example.
Such a perforator may be affected by heat generated in the image forming unit, wherein the heat may be generated when the image forming unit conducts an image transfer process, for example.
Such heat may affect a plurality of parts in the perforator, and may cause a temperature variation between the plurality of parts in the perforator.
For a reciprocal type perforator, a sheet is temporarily stopped and then pressed to the die frame to perforate a hole on the sheet with a reciprocal movement of the blade through the die hole of the die frame, wherein the sheet may receive some heat energy during the image forming process in the image forming unit.
Accordingly, the die frame may have a relatively higher temperature compared to the guide frame. In addition, the die frame and the guide frame may be firmly fixed with each other by a rivet or the like to maintain a preciseness of perforation.
Therefore, if a temperature variation occurs between the die frame and guide frame, one of the die frame and the guide frame may be deflexed.
Such deflection may be observed as an elongation of the die frame due to a temperature increase of the die frame. Such elongation may occur to the die frame because the die frame and the guide frame are fixed firmly, as discussed above.
Such deflection may occur in either one of two directions depending on a shape of the guide frame and the die frame. One direction is a parallel direction with respect to the transport direction of sheet, and another direction is a vertical direction with respect to the transport direction of sheet.
If the die frame deflects in a parallel direction with respect to the transport direction of sheet, the guide hole and die hole may be deviated from the aligned condition.
If such deviation is significant such deflection may hinder the pass-through of the blade in the die hole, and may degrade the perforation quality.
Furthermore, if the blade can not pass through the die hole smoothly, the blade may become overloaded, by which the image forming system may stop the movement of blade, and then an operation of the image forming system may be stopped.